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From: kwe@bu-it.bu.edu (Kent England)
Newsgroups: comp.dcom.sys.cisco
Subject: Re: Is it possible to configure two default routes on a Cisco router ?
Message-ID: <76774@bu.edu.bu.edu>
Date: 12 Mar 91 21:59:36 GMT
References: <19012@imag.imag.fr>
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Reply-To: kwe@bu.edu
Organization: Boston University Information Technology
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> From: laforgue@imag.fr (Pierre LAFORGUE)
> Newsgroups: comp.dcom.sys.cisco
> Date: 12 Mar 91 07:48:57 GMT
> 
> I need to configure:
> - for the network A a default route via a machine of C
> - for the network B a default route via a machine of D
> ...
>                                 ------------
> ---------- subnet A.1 ---------|            |
> ---------- subnet A.2 ---------|            |---......----- network C
> ---------- etc        ---------|   Cisco    |
> ---------- subnet B.1 ---------|            |---......----- network D
> ---------- subnet B.2 ---------|            |
> ---------- etc        ---------|            |
>                                 ------------
> How could I do that ?

	What is usually done in your situation is to receive all route
advertisements known to routers on nets C and D into the cisco (while
sending nets A, B, and C or D) and send only a default to nets A and
B.  This creates a large routing table in the cisco which does not use
a default route itself, while relieving the local nets A and B of
having large tables by using a default pointing to the cisco.  If you
don't want the broadcast load on nets C and D, you may be able to use
EGP between the cisco and the authoritative routers on nets C and D.

	You also need to decide whether the cisco can be a route
between C and D.  If so, then those nets need those route
advertisements, like the cisco does.  In this case, have the
authoritative routers broadcast all known nets onto their nets C and D
for the cisco and all hosts.  Then no one on nets C and D uses
default.

	--Kent